Experimental evidence of inversion-layer mobility lowering in ultrathin gate oxide metal-oxide-semiconductor field-effect-transistors with direct tunneling current

In this paper, the results of the direct measurement of inversion-layer mobility for metal-oxide-semiconductor field-effect-transistors (MOSFETs) with ultrathin gate oxides, based on the split C-V method are reported. It was demonstrated that inversion-layer electron mobility can be accurately measured for MOSFETs with gate oxide thickness of down to 1.5 nm by the split C-V method with modified measurement of drain conductance under optimum device size and Measurement conditions, It was found that, when gate oxide thickness is less than 3 rum, the mobility deceases in the low surface carrier concentration (effective field) region with a decrease in gate oxide thickness and that this mobility lowering becomes smaller in the higher surface carrier concentration (effective field) region. It was also found that mobility limited by some additional scattering observed in thin gate oxides has almost no surface carrier concentration dependence.